(1) Field of the Invention:
This invention relates to a method for recording information optically, a method for reading the recorded information optically, and optical recording media for use in recording information optically and reading the recording information optically.
(2) Description of the Prior Art:
In recent years, it is more and more strongly desired to record information (for example, images or voices) and reproduce the recorded information at high speed, at high density and with ease. In fact, a variety of recording methods and recording media associated therewith have been proposed and some of them are being used for practical purposes.
Among these recording media, the so-called optical disks which typically use laser light for the purpose of reading recorded signals are expected to find general acceptance, because they can record information on the medium at an extremely high density and read the desired recorded information from any location on the medium.
Conventionally, typical recording and reading systems for use with optical disks are based on the method in which information is recorded by forming minute pits in a surface of light-transmissive plastic material and the recorded information is read by forming a reflective layer on the pit-bearing surface (e.g., by vacuum evaporation of metal), illuminating the medium with a spot beam of laser light, generally from the opposite side, and using a photodiode or the like to detect changes in the amount of reflected light due to the diffraction of light at the pit edges and convert them into electric signals.
However, since this method involves the creation of very minute, physical configurations having a dimension of 1 .mu.m or less (i.e., pits) by physical means such as injection molding, compression molding or the like, a number of shortcomings are recognized with respect to recording accuracy and productivity. Specifically, the fabrication of a stamper used for the transfer of signal pits requires a highly complicated procedure and, moreover, the stamper has a limited working life because it tends to become clogged during repeated use for molding purposes. In addition, this method has the disadvantages of encountering difficulties in forming highly accurate pits under certain molding conditions, requiring an expensive molding machine, and imposing great restrictions on the molding properties of the plastic material used as a base material.
Accordingly, it is desired to develop a novel optical recording medium based on a new signal input/output principle which can overcome the above-described disadvantages.